A linear collider will be constructed as an apparatus for creating a state of Big Bang by the collision of positrons and electrons (International Linear Collider Project). The linear collider uses a hollow tube 100 made of niobium, which is provided with flanges 101a and 101b at both ends, and has a diameter changing periodically in an axial direction, as shown in FIG. 13. There are requirements to obtain a predetermined effect in this experiment, and one requirement is that the inner surface of the niobium hollow tube 100 is to be smooth.
The hollow tube 100, however, is subjected to an excessive pressure and heat at the formation, so that a texture of an inner surface becomes distorted non-uniformly. If this surface status is left alone, the electric properties and the magnetic properties become uneven, too, with the result that it is impossible to impart a predetermined speed to the electrons and the positrons. Therefore, methods for polishing the inner surface of the hollow tube in a predetermined thickness have been developed as a countermeasure against such problem.
As the polishing method for the niobium hollow tube, there are two kinds of polishing methods, namely, a method for polishing chemically (hereinafter referred to a “chemical polishing”) and a method for polishing electrochemically (hereinafter referred to an “electrolytic polishing”).
According to the chemical polishing disclosed in Japanese Unexamined Patent Application Publication No. 57-114669, a mixture of fluoric acid, sulfuric acid and water is used as a polishing liquid, and a niobium member is immersed in the mixture, whereby the entire surface is chemically polished to be smooth. As a polishing liquid for the same purpose, it is also well-known that a mixture of fluoric acid, phosphoric acid and nitric acid is used. In either of the above methods, the whole of the hollow tube is immersed in the polishing liquid, so that the operation becomes very simple. However, the outer surface of the hollow tube, which is not required to be polished, is polished concurrently, and it accelerates the unnecessary contamination, the aging, and the deterioration of the polishing liquid. Moreover, there is a problem that a polishing amount differs notably depending on an immersion direction of a polishing object.
Such incident is involved in an action of stirring the polishing liquid by a produced gas, and the produced gas sticks to the inner surface of the tube due to the shape of hollow tube and damages the polished appearance, which results in many drawbacks.
With respect to the electropolishing, there are following examples.
Japanese Examined Patent Application Publication No. 55-12116 discloses an intermittent electropolishing wherein, the niobium hollow tube is placed keeping both openings in horizontal, a lower half part of the niobium hollow tube is partially immersed in the polishing liquid composed of the fluoric acid, the sulfuric acid and the water. While maintaining the partial immersion, the partial electropolishing is performed by turning on the power for a short time. And after the electricity went off, the tube is rotated to dissolve and remove an oxide film. These steps are executed repeatedly.
In the above-mentioned method, the outer surface of the hollow tube not to be polished is polished at the same time that the inner surface is polished, as a result, the unnecessary dissolving loss of the hollow tube occurs and the polishing liquid is consumed unnecessarily and contaminated. Moreover, the polishing unevenness occurs due to the intermittent polishing, and the operation is very dangerous because of handling the fluoric acid that is high volatile and produces toxic gas, and the sulfuric acid that is a high pyrogenic substance.
The invention disclosed in Japanese Unexamined Patent Application Publication No. 61-23799 is configured to perform the continuous electrolysis in the state of the partial immersion by supplying the polishing liquid from nozzles connected with a liquid feed pipe while rotating the niobium hollow tube. In this configuration, the polishing time can be reduced and the unnecessary dissolution of the niobium member can be eliminated, and therefore, it is possible to suppress the unnecessary contamination and consumption of the polishing liquid.
However, since it is configured that the nozzles provided to the liquid feed pipe are opened in the polishing liquid and the polishing liquid is discharged into the stored polishing liquid, the difference between the flow rates of the polishing liquid appears in the state of the polishing, and the unevenness of the polished appearance occurs on the inner surface of the niobium hollow tube, which is a problem, too.
The invention disclosed in Japanese Unexamined Patent Application Publication No. 11-350200 is the basically same as Japanese Unexamined Patent Application Publication No. 61-23799, but the nozzles provided to the liquid feed pipe is configure to be opened toward an upper side of the polishing liquid, the side opposite to the side to be polished, so as not to flow the polishing liquid direct into the stored polishing liquid. According such configuration, the invention realizes the uniform polishing.